1. Technical Field
The disclosure relates to a position measuring method for a reference surface at the time when a workpiece is machined.
2. Description of Related Art
A machine tool having a function of setting a measurement reference point of a workpiece is known. The machine tool is configured to obtain center coordinates of the workpiece and set the center coordinates as a measurement reference point for measuring, for example, a shape of the workpiece (see Japanese Patent Application Publication No. 2010-89182 (JP 2010-89182 A)). The machine tool sets a measurement reference position of the workpiece according to the following procedure.
First, a workpiece having a machining surface that is symmetric with respect to each of two lines perpendicular to each other is disposed such that the axes of a machine coordinate system are parallel to the two lines. Next, a spherical measuring portion of a probe of an on-machine measurement apparatus is moved relative to the workpiece toward an end surface of the workpiece from a position on the machining surface of the workpiece along a first line that is parallel to one of the two lines.
After the spherical measuring portion moves away from the end surface of the workpiece, coordinates at the time when a moving speed of the probe in its axial direction reaches a predetermined speed are stored. Then, the same procedure is performed with regard to a second line, which is parallel to the other one of the two lines, and coordinates are stored. Then, midpoints are obtained from the stored coordinates. The obtained midpoints are the center coordinates of the workpiece, and may be set as a measurement reference position of the workpiece.